Aluminum plate-fin heat exchanger utilizing titanium separator plates

ABSTRACT

A plate fin heat transfer device utilizes titanium plate members and aluminum dividers. The solid bar may be titanium, aluminum or an alloy of either. The titanium plate members may have a thermal conductivity of approximately 50 or 100 BTU/Hr/ft/F/in and dramatically reduce matrix conduction of heat within the plate members. The plate members may be as thin as approximately 0.002 inches while providing the necessary strength to avoid leakage during or after the manufacturing process. The advantageous thinness satisfies weight and volume parameters critical to an aircraft.

BACKGROUND OF THE INVENTION

The present invention generally relates to apparatus and methods for improving the effectiveness of plate heat exchangers and, more particularly, to apparatus and methods of reducing matrix conduction effects in plate heat exchangers.

In the aerospace industry, an aircraft typically has an environmental control system that may include various heat transfer devices. These heat transfer devices may include plate fin heat exchangers. The desire to utilize high thermal conductivity materials for the heat exchanger and minimize the weight of the aircraft has lead to the use of aluminum plate members in the plate fin heat exchangers. Light weight high effectiveness heat exchangers are often made entirely of aluminum for its high thermal conductivity. In this regard the term “aluminum” means commercially pure aluminum or an alloy where aluminum is the largest constituent.

There is a greater driving force for heat transfer when the temperature difference of two mating fluids is greater. As a result of the high thermal conductivity of aluminum, as seen from FIG. 1 wherein arrows represent heat flux and wherein the wavy lines represent matrix conduction of heat within the plate members, total heat transfer across the plate members 12 from fluid 11 to fluid 13 is reduced and the functioning of the heat exchanger is reduced when the matrix conduction is high because the sum of the average local temperature difference between fluid 11 and fluid 13 over the entire heat exchanger is reduced by the matrix conduction. Overall effectiveness of the heat exchanger is reduced when heat runs along the plate member 12 away from the local area toward another area in the heat exchanger matrix such as the solid bars resulting in a less advantageous path from fluid 11 to fluid 13. This can occur when heat runs along plate member 12 from a hot end of plate member 12 to a cold end of plate member 12 instead of crossing plate member 12. Another parameter that must be satisfied in constructing heat transfer systems in aircraft is minimizing volume since space is limited.

As can be seen, there is a need to have a heat transfer device in an aircraft that minimizes volume while still minimizing weight and that avoids the deleterious effects of matrix conduction.

SUMMARY OF THE INVENTION

In one aspect of the present invention, there is presented a plate fin heat transfer device, comprising a first titanium plate member and a second titanium plate member, the first and second titanium plate members each having a thickness of between approximately 0.002 inches and approximately 0.125 inches and having a top edge; a solid bar joining the top edges of the first and second titanium plate members; a set of aluminum dividers joined between the first and second titanium plate members, the dividers defining a series of passageways; and a series of alternate passageways alongside an outside surface of the first titanium plate member and alongside an outside surface of the second titanium plate member.

In a further aspect of the invention, there is presented a method of exchanging heat using a plate fin heat transfer device, comprising directing a heating fluid alongside a surface of a first titanium plate member so as to cause convection of heat energy from the heating fluid to the first titanium plate member, the first titanium plate member joined to a second titanium plate member by aluminum dividers that define a series of passageways between the first and second titanium plate members, a solid bar of aluminum joined to a top edge of the first and second titanium plate members; directing a heating fluid alongside a surface of the second titanium plate member so as to cause convection of heat energy from the heating fluid that is alongside the surface of the second titanium plate member to the second titanium plate member; and directing a cooling fluid through the series of passageways to cause a heat flux from the first and second titanium plate members to the cooling fluid with matrix conduction that is reduced compared to a plate member made of aluminum such that overall heat transfer conductance of the heat transfer device is improved by approximately 5% to 50% compared to a heat transfer device with plate members made of aluminum.

In another aspect of the invention, there is presented a plate fin heat transfer device, comprising a plurality of titanium plate members having a thermal conductivity of no more than approximately 120 BTU/Hr/ft/F/in, each of the plate members also being thinner than 0.012 inches, the plate members having a top edge; a set of aluminum fins brazed between two of the plurality of titanium plate members, the fins defining a series of passageways for a first fluid to pass through; solid bars joining top edges of any two of the plate members, the solid bars made of aluminum, titanium, an alloy of aluminum or an alloy of titanium; and a second fluid having a different temperature than the first fluid, the second fluid directed alongside an outside surface of a first titanium plate member and directed alongside an outside surface of a second titanium plate member.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, descriptions and claims

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a prior art heat transfer device showing matrix conduction through plate members;

FIG. 2 is a partially cut perspective view of a plate fin heat transfer device core with its housing partially cut away, in accordance with the present invention;

FIG. 3 is a sectional view of the heat transfer device of FIG. 2;

FIG. 4 is a sectional view of plate fin heat transfer device of the present invention showing reduced matrix conduction; and

FIG. 5 is a flow chart showing a method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

The present invention generally provides a plate fin heat exchanger for use where matrix conduction is a problem because the heat exchanger is required to have very high effectiveness usually in systems where there is low flow velocity. In the plate fin heat exchanger of the present invention, the plate members may be entirely titanium. The remainder of the heat exchanger may be aluminum.

In contrast to the prior art, which does not use titanium plate members in an otherwise aluminum heat exchanger, the heat exchanger of the present invention may utilize plate members that are titanium. In further contrast to the prior art, in which matrix conduction within the aluminum plate members negatively affects the performance of the heat transfer device, the plate fin heat exchanger of the present invention may minimize matrix conduction. In further contrast to the prior art, which utilizes plate members that maximize thermal conductivity, which is intuitive for heat transfer devices, the plate fin heat exchanger of the present invention may utilize plate members made of a lower thermal conductivity material than aluminum. In further contrast to the prior art, in which the entire heat exchanger may be aluminum, the present invention may utilize plate members of titanium such that lower matrix conduction results in greater overall heat transfer efficiency so that volume may be reduced an important consideration for an aircraft. Furthermore, in contrast to the prior art plate fin heat exchangers, for example those made of all-aluminum, in which the weight cannot be fully minimized because, despite aluminum being lightweight, aluminum plate members need to be thicker to have the necessary load capacity, the plate fin heat exchanger of the present invention saves weight, since, although its titanium plate members are denser, they can be thinner than conventional aluminum plate members due to their superior strength. Moreover, the overall size of the plate fin heat exchanger of the present invention may be reduced by an amount in the order of approximately 5% to approximately 20% by reducing the size of any of its three dimensions (i.e. stack height, etc.) and this may save a significant amount of weight. Specifically, in further contrast to the prior art, in which leakage and holes would likely arise during brazing of plate members if such plate members were manufactured having a thickness of only 0.01 inches, in the plate members of the heat exchanger of the present invention, the plate members are durable enough that leakage may not occur (or may more easily meet the acceptance limit of leakage for the device) even though the plate members may be as thin or thinner than 0.01 inches.

FIG. 2 shows a partially cut perspective view of a plate fin heat transfer device 10 whose housing has been partially cut away. Device 10 may comprise a series of plate members 20, as well as dividers 30 and solid bars 40. Dividers 30 may be called fins and are made in a myriad of configurations known to those skilled in the art. Dividers may be made typically from formed sheet metal but may also be fabricated from other structures. Plate members 20 may be made entirely of titanium. In this regard, the term “titanium” means commercially pure titanium or an alloy of titanium where titanium is the largest constituent. It is understood that plate members 20 are sometimes also referred to in the industry as “tubesheets”, as “tube plates”, as “parting sheets” or as “separator plates”.

As seen from FIG. 2, each of titanium plate members 20 may have a top edge 29 to which a solid bar 40 may attach. Thus, solid bar 40 may join top edges 29 a, 29 b of the two titanium plate members 22, 24 and may join top edges of any two other titanium plate members 20. Solid bar 40 may also be made of aluminum, titanium or an alloy of aluminum or titanium. Of course, plate fin heat transfer device 10 may contain much more than two plate members. Accordingly, when plate members 20 are referred to as including first and second titanium plate members, these may be arbitrarily chosen to represent any two titanium plate members that have fins adjoining them.

As seen from FIG. 2, plate fin heat transfer device 10 may also have a set of aluminum fins 30 brazed between the first and second titanium plate members 22, 24. Fins 30, for example vertical fins 30 a, may define a series of passageways 31 for a first fluid 51, such as a cooling fluid 60 to pass through. As seen from FIG. 2, alternate sets of fins, for example horizontal fins 30 b on the other side of first plate member 22 or second plate member 24, may define a series of alternate passageways 33 and may have a second fluid 52 such as a heating fluid 50 passing through these fins 30 b. It should be appreciated that while the first fluid may be a heating fluid and the second fluid may be a cooling fluid it may also be true that the first fluid may be a cooling fluid and the second fluid may be a heating fluid.

As can be seen from FIG. 3, first plate member 22 and second plate member 24 may each contain a plate member layer 26, which may be made entirely of titanium, and may each also contain braze alloy layers 28 which may be made of an aluminum braze alloy. First and second titanium plate members 22, 24 each may have a thickness from about 0.002 inches to about 0.125 inches and typically approximately 0.006 inches or even less. Titanium plate members 20, even at a thickness of 0.002 inches, may have the strength needed to withstand breakage and leakage during brazing and afterwards.

As seen further from FIG. 3, heating fluid 50 may be directed alongside an outside surface 21 a of the first titanium plate member 22 and invention also envisions a method 100 of exchanging heat using a plate fin heat exchanger. One step 110 of method 100 comprises directing a first fluid, such as a heating fluid, alongside a surface of a first titanium plate member so as to cause convection of heat energy from the heating fluid to the first titanium plate member. In step 110 the first titanium plate member may be joined to a second titanium plate member by aluminum dividers that define a series of passageways between the plate members. Furthermore, a sold bar, such as made of aluminum, may be joined to a top edge of the first and second titanium plate members. An additional step 120 of method 100 involves directing a heating fluid, which may or may not be the same heating fluid, alongside a surface of a second titanium plate member so as to cause convection of heat energy from that heating fluid to the second titanium plate member. A further step 130 of method 100 involves directing a second fluid, which may be a cooling fluid, through the series of passageways to cause a heat flux from the first and second titanium plate members to the cooling fluid with matrix conduction that may be less than if the plate member were aluminum such that heat transfer conductance of the heat exchanger may be improved by 5% or more. For example, heat transfer conductance may be improved in certain cases by approximately 10%, 20%, 30%, 40% or 50%.

It should be appreciated that the fluid running through fins 20 may also be a heating fluid and the cooling fluid may be the fluid that is directed alongside the outer surface of the titanium plate members. In that case, the cooling fluid alongside one titanium plate member may or may not be the same cooling fluid that is directed alongside an outer surface of the second titanium plate member.

It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims. alongside an outside surface 21 b of the second titanium plate member 24. As seen from FIG. 4 wherein arrows represent heat flow by convection, heat from heating fluid 50 may thereby conduct into first and second titanium plate members 22, 24 and may then conduct from plate members 20 into cooling fluid 60.

FIG. 4 shows that with the titanium plate members 20 there may be less matrix conduction of heat within the first and second titanium plate members 20 from the hot end of plate member 20 to the cold end of plate member 20. The amount of matrix conduction within titanium plate members 20 may be significantly less than would be the case were the plate members made of aluminum, as in the prior art heat transfer device of FIG. 1.

Titanium plate members 20 may be made of various types of titanium such as titanium-CP-70 having a thermal conductivity of approximately 118 BTU/Hr/ft/F/in, titanium-6-4 having a thermal conductivity of approximately 50 BTU/Hr/ft/F/in or titanium-21S, which has a thermal conductivity of approximately 53 BTU/Hr/ft/F/in. Accordingly, the thermal conductivity of the plate members 20 may be significantly lower than for aluminum plate members, which may have a thermal conductivity of over 1000, for example approximately 1070 BTU/Hr/ft/F/in for 6061 aluminum and approximately 1370 BTU/Hr/ft/F/in for 6951 aluminum. Notwithstanding that, each of the plate members 20 may be significantly stronger than aluminum plate members of equal size. Size here refers to the length and width of the plate member (i.e. the dimensions other than the thickness of the plate member). Each of the plate members 20 may also be thinner than 0.012 inches for example, as thin as from about 0.002 inches.

As is known in the industry, the heating and cooling fluids passages in the plate fin heat transfer device may be in various configurations, including a counterflow configuration, a crossflow configuration, a multi-pass crossflow configuration, or any other well known configuration.

As can be seen from FIG. 5, which is a flow chart, the present 

1. A plate fin heat transfer device, comprising: a first titanium plate member and a second titanium plate member, the first and second titanium plate members each having a thickness of between approximately 0.002 inches and approximately 0.125 inches and having a top edge; a solid bar joining the top edges of the first and second titanium plate members; a set of aluminum dividers joined between the first and second titanium plate members, the dividers defining a series of passageways; and a series of alternate passageways alongside an outside surface of the first titanium plate member and alongside an outside surface of the second titanium plate member.
 2. The plate fin heat transfer device of claim 1, wherein matrix conduction of heat within the plate members is less than with an aluminum plate member.
 3. The plate fin heat transfer device of claim 1, wherein the sold bar is made of aluminum.
 4. The plate fin heat transfer device of claim 1, wherein the plate members contain an aluminum braze alloy.
 5. The plate fin heat transfer device of claim 1, wherein the solid bar is made of an alloy of aluminum or titanium.
 6. The plate fin heat transfer device of claim 1, wherein the plate members themselves do not leak or have leakage that meets the acceptance limit of leakage for the device.
 7. A method of exchanging heat using a plate fin heat transfer device, comprising: directing a heating fluid alongside a surface of a first titanium plate member so as to cause convection of heat energy from the heating fluid to the first titanium plate member, the first titanium plate member joined to a second titanium plate member by aluminum dividers that define a series of passageways between the first and second titanium plate members, a solid bar of aluminum joined to a top edge of the first and second titanium plate members; directing a heating fluid alongside a surface of the second titanium plate member so as to cause convection of heat energy from the heating fluid that is alongside the surface of the second titanium plate member to the second titanium plate member; and directing a cooling fluid through the series of passageways to cause a heat flux from the first and second titanium plate members to the cooling fluid with matrix conduction that is reduced compared to a plate member made of aluminum such that overall heat transfer conductance of the heat transfer device is improved by approximately 5% to 50% compared to a heat transfer device with plate members made of aluminum.
 8. The method of claim 7, including directing a heating fluid alongside a surface of the second titanium plate member so as to cause convection of heat energy from the heating fluid that is alongside the surface of the second titanium plate member to the second titanium plate member.
 9. The method of claim 7, wherein the heat transfer conductance is improved by 40% or more compared to a device with aluminum plate members.
 10. The method of claim 7, wherein the heat transfer conductance is improved by 30% or more compared to a device with aluminum plate members.
 11. The method of claim 7, wherein the heat transfer conductance is improved by 20% or more compared to a device with aluminum plate members.
 12. The method of claim 7, wherein the heat transfer conductance is improved by 10% or more compared to a device with aluminum plate members.
 13. The method of claim 12, wherein the heat transfer conductance is improved by 5% or more compared to a device with aluminum plate members.
 14. The method of claim 7, wherein the heat transfer conductance is improved by 50% or more compared to a device with aluminum plate members.
 15. A plate fin heat transfer device, comprising: a plurality of titanium plate members having a thermal conductivity of no more than approximately 120 BTU/Hr/ft/F/in, each of the plate members also being thinner than 0.012 inches, the plate members having a top edge; a set of aluminum fins brazed between two of the plurality of titanium plate members, the fins defining a series of passageways for a first fluid to pass through; solid bars joining top edges of any two of the plate members, the solid bars made of aluminum, titanium, an alloy of aluminum or an alloy of titanium; and a second fluid having a different temperature than the first fluid, the second fluid directed alongside an outside surface of a first titanium plate member and directed alongside an outside surface of a second titanium plate member.
 16. The plate fin heat transfer device of claim 15, wherein the heating and cooling fluids passing through the plate fin heat transfer device are in a counterflow configuration.
 17. The plate fin heat transfer device of claim 15, wherein the titanium plate members have a thermal conductivity less than half that of the aluminum fins.
 18. The plate fin heat transfer device of claim 15, wherein the titanium plate members have a thermal conductivity of less than 60 BTU/Hr/ft/F/in.
 19. The plate fin heat transfer device of claim 15, wherein the first fluid is a heating fluid and the second fluid is a cooling fluid.
 20. The plate fin heat transfer device of claim 15, wherein the first fluid is a cooling fluid and the second fluid is a heating fluid. 